1. Field of the Invention
The present invention relates generally to chemical mechanical polishing (CMP) process control, and more particularly to a CMP process control feature suitable for both optical microscope inspection and critical dimension scanning electron microscope inspection and measurement.
2. Description of the Prior Art
In the fabrication of thin film devices such as magnetic heads for hard disk drives, one or more chemical mechanical polishing (CMP) steps are often undertaken to remove portions of existing surface features and obtain a generally flat, smooth surface upon which to fabricate further thin film layers and structures. As is well known to those skilled in the art, where a CMP step is undertaken above delicate structures, such as the sensor layer structure of a read head portion of a magnetic head, accurate process control must be maintained, such that the CMP step is conducted for sufficient time to remove the unwanted surface layers or features, while not overpolishing and removing the desired delicate structures. The delicate surface structures are so small, generally measuring less than a micron, that process control must typically be conducted using a critical dimension scanning electron microscope (CDSEM). The use of the CDSEM for process control increases equipment expenses and is time consuming, and therefore slows manufacturing throughput during the fabrication process. Additionally, because skilled operators are required to operate a CDSEM properly, the expense of the fabrication process is increased. The present invention provides a solution to these problems by enabling the use of an optical microscope which generally has a small feature limit of approximately 20 microns in process control related to these structures that are too small to be viewed by the optical microscope.